Field of the Invention
The present invention relates to a welding process for a titanium material (hereinafter referred to as Ti) and a copper (hereinafter referred to as Cu) material. This invention also relates to a sputtering target or a backing plate for use in a sputtering target, based on a Tixe2x80x94Cu composite plate welded by the aforementioned welding process.
The sputtering process is well known for forming a thin film to be used on an integrated circuit. A sputtering target is used in processes of physical sputtering (PVD) and reactive sputtering. The sputtering target is composed of a target member upon which ions are impacted, and a backing plate at its rear for supporting the target member. Concretely, it is known that a target member composed of a chromium (hereinafter referred to as Cr) material, a Ti material or an Al material is bonded (brazed) with an indium (hereinafter referred to as In) material, on a backing plate composed of a Cu material, a Ti material or an aluminum (hereinafter referred to as Al) material.
For example, it is disclosed in Japanese patent Application Laid-Open No. 6-293963 that a Ti material is used as the backing plate.
It is disclosed in Japanese Patent Application Laid-Open No. 6-293963 and Japanese patent Application Laid-Open No. 3-140464 that the bonding of the target member is conducted by using the In material.
The target member is bonded using an In material as a solder with the aforementioned Ti material being used as a backing plate. The surface of the Ti material is covered with a strong thin oxide film (passive state film) due to exposure to atmosphere, moisture and so on. This passive state film is so strong that it is extremely difficult to remove. It is hard to react to other metals so that wettability of the Ti surface is so poor that it extremely difficult to conduct bonding operations using. Wettability is the extent to which a solid is wetted by a liquid, measured by the force of adhesion between the solid and the liquid. In order to avoid such difficulty, in the aforementioned Japanese Patent Application Laid-Open No. 6-293963, the Cu is thermally sprayed (sprayed as a liquid) upon the surface of the backing plate made of the Ti material, to thereby improve the wettability of the In material. Thermal spraying with Cu substantially increases the manufacturing cost of the sputtering target.
The same problem is caused even in the recycling of the sputtering target when the target member is removed from the used sputtering target, and used again with a new target member bonded to the backing plate. In the Japanese Patent Application Laid-Open No. 6-116706, surface processing of the Ti material is proposed which consists of heating about one hour at 700xc2x0 C. in vacuum, with the Ti material coated with, for example, Cu powder, so as to improve the adherence strength by diffusing the Cu on the surface of the Ti. The reaction layer is fragile because it is, at most, several xcexc thick, and because the reaction takes place in a solid phase. Thus, it is necessary to again conduct surface processing for recycling the sputtering target.
When Ti material is used as the backing plate, it is preferable to have the Cu material welded on the surface to improve the wettability during bonding of the target member. In this case, it is important to establish a welding process capable of welding with high quality and low cost. The same thing can be said also in using the Cu material as the backing plate, and the Ti material as the target member. When the backing plate and the target member are both composed of a Ti material, it is helpful in practical use when both can be welded through the Cu material.
The inventors conducted various tests using the eutectic reaction of the Tixe2x80x94Cu in connection with the welding property between the Ti material and the Cu material. In the test 1, a Cu foil of 2 mm thickness was placed on the Ti material to conduct 30 minutes heating (non-pressure) at 850xc2x0 C. lower than the eutectic temperature (887 C) of the Tixe2x80x94Cu. As the result, the reaction of the Tixe2x80x94Cu was observed only in the portion of 20% in the area ratio, with remaining 80% remaining unreactive. Thus, according to the welding method, an object of obtaining the better welding result cannot be achieved. As the test 2, 30 minutes heating was conducted at 900xc2x0 C. higher than the aforementioned eutectic temperature with a welding Cu plate of 2 mm thickness being placed between the Ti material and the Cu material. As the result, as shown in FIG. 1, a, Ti2Cu layer, TiCu layer were mixed in spots on the Ti material, with the welding Cu plate being completely molten.
As described above, in the prior art process of forming the Cu welding portion by using the eutectic reaction of the Tixe2x80x94Cu, uniformity of the reaction cannot be obtained in a temperature area lower than the eutectic temperature, thus it is not possible to have homogeneous welding. When the processing operation is conducted at a temperature region higher than the eutectic temperature to obtain uniformity of the reaction, the liquid phase occurs too rapidly, and the reaction between the Ti and the Cu also are promoted rapidly. The liquid phase increases until the Cu completes the reaction with considerable penetration of the Ti into the liquid phase including the Cu. As a result extremely fragile intermetallic compounds (Ti2Cu, TiCu) exist in the welding region in amounts that degrade welding quality.
This invention is provided to overcome the aforementioned defects.
An object of this invention is to provide a welding process between a Ti material and a Cu material capable of better welding quality.
Another object of this invention is to provide a Tixe2x80x94Cu composite plate improved as described above.
A still further object of this invention is to provide a sputtering target which reduces manufacturing cost by using the composite plate as a backing plate of a sputtering target.
A further object of this invention is to reduce the recycle cost of the sputtering target.
Briefly stated, the present invention provides a welding process for welding a Cu material to a Ti material which includes interposing a tertiary component between the Ti material and the Cu material. The tertiary component is of a type of metal that, with Cu, forms a compound which is liquified at a temperature below the eutectic temperature of Ti and Cu. The above materials are heated and welded at temperature of (700 through 887xc2x0 C.). The temperature selected is below the eutectic temperature of the Ti and Cu. The finished material forms a sputtering backing plate for a sputtering. A target member, bonded to the Cu material side of the backing plate, completes the sputtering target. In one embodiment, the proportion of the tertiary metal is achieved by controlling a thickness of the tertiary metal deposited on the Cu material. In another embodiment, the proportion of the tertiary metal is achieved by controlling the thickness of a layer of powder of the tertiary material deposited between the Cu and Ti materials.
According to an embodiment of the invention, there is provided a process for welding a Ti material and a Cu material comprising. interposing a welding Cu material, including a tertiary metal as a component, between a Ti material and a Cu material, said tertiary material being of a type which performs one of the following:
reduces a three-element eutectic temperature of the Ti, the Cu and said tertiary metal below a eutectic temperature of said Ti and the Cu; and
produces a reaction which causes a liquid phase at a temperature that is lower than a two-element eutectic temperature between the Ti material and the Cu material, heating the Ti material and the Cu material to said temperature wherein solid and liquid coexist; and
maintaining said temperature long enough to form a welding portion.
According to a feature of the invention, there is provided a Tixe2x80x94Cu composite plate having a welding portion formed by the process of the preceding paragraph.
According to a further feature of the invention, there is provided a process for forming a plate including interposing a tertiary metal between a Cu material and a Ti material, said tertiary metal being of a type which reacts with at least one of Cu and Ti to reduce a melting temperature below a temperature of an eutectic temperature of said Cu and Ti material, and holding said materials at said temperature for a time sufficient to obtain welding.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.